1. Field of the Invention
The present invention concerns a system and method for monitoring the performance of remote factory located chiller units, and in particular, to a system and method which enable the precognition of a refrigerant leak, or insufficiency of a refrigerant, in the refrigeration circuit of chiller units, for enabling preventative maintenance to be performed thereon.
2. Description of the Related Art
Systems for performing remote maintenance on various types of industrial equipment are known. Remote maintenance technology is a technique for monitoring operation and predicting problems of equipment located at customer sites from a monitoring and maintenance facility, thus allowing one to obtain equipment operating data. In such systems, various operational parameters of the equipment installed in remote locations are sensed and transmitted in digital form over a network to a server monitoring and maintenance facility. At the server monitoring and maintenance facility, the parameters are collected and monitored over time and, on the basis of various protocols, if one or more of the sensed parameters suggests a current or potential future malfunction in the equipment, maintenance staff can be dispatched to the remote locations where the equipment is located, in order to effect repairs, perform routine maintenance, and the like. One particular type of industrial equipment which is widely used is known as axe2x80x9cchillerxe2x80x9d unit. The outer aspect of a known type of chiller unit is shown in FIG. 1. The chiller unit 10 is basically a portable refrigeration unit having a refrigeration circuit through which a refrigerant gas medium such as R134a, R22, R404A, or the like, is circulated in a known manner. In addition to the refrigeration circuit, a cooling medium, usually water, is circulated both internally and externally of the chiller unit 10 through a cooling medium circulating circuit, wherein the cooling water undergoes thermal exchange with the refrigeration circuit for cooling the water. The cooled water is then pumped centrifugally out of the chiller unit 10 through a cooling conduit making up the external part of the cooling medium circulating circuit. More specifically, respective ends of the cooling conduit are connected to cooling medium inlet and outlet connections 20 and 30 on the chiller unit 10, wherein the cooling medium circulating conduit is installed in a circuitous pattern throughout the location where it is necessary to maintain a predetermined cooled condition, such as in semiconductor manufacturing chambers, computer hardware installations, or any other type of equipment for which controlled cooling is required. The chiller unit 10, as shown in FIG. 1, includes various controls and/or indicator lights (generally designated at 40) thereon for controlling chiller operation. The operating temperature of the cooling medium produced from chiller unit may be displayed using a gauge 70. Such chiller units 10 are generally portable via casters 50 and are intended to be located in close proximity to the customer facility in which the cooling conduits are installed and used, the units being fixed in place by adjustable positioning feet 60.
A typical maintenance problem with any refrigeration circuit, including the above-described chiller units, is that of refrigerant gas leakage. In the context of chiller units, the most serious problem, of course, is when the unit fails to cool properly, and refrigerant gas leakage is one of the primary causes for failure to cool. The demands of precision manufacturing, such as in semiconductor production facilities, require precise and unfailing temperature controls. Unfortunately, it is generally difficult to effectively diagnose problems of refrigerant gas leakage.
Currently, two methods are used to detect refrigerant gas leakage in chiller units. The first is to directly trace the gas leak using a refrigerant gas leakage detector. Secondly, it is possible to diagnose gas leakage by reading the refrigerant gas pressure. Both of these methods have disadvantages. Namely, the detecting devices tend to be expensive. In addition, the devices must be used at the location of the chiller unit in order to directly detect a leak or to detect refrigerant gas pressure. Such devices are not easily capable of transmitting the detected data to other locations. Moreover, such devices, while useful for detecting the source of a refrigerant gas leak, do not enable ongoing observation of a refrigeration circuit in such a way as to enable predictive maintenance to be performed, namely, to tell when a refrigerant gas leak or insufficiency of refrigerant is likely to happen, and perform the necessary preventative maintenance to correct the problem. before it becomes serious.
The temperature in connection with the evaporator in a refrigeration circuit has been measured as a method for detecting insufficiency of the refrigerant. Prior art references which employ such methods, in various forms, shall be discussed below. Typically such systems have been proposed primarily for use in automobiles.
Japanese Laid-Open Application No. 63-32271 proposes that the evaporation temperature of a refrigerant medium should be detected before and after starting a compressor, wherein a gas leak can be detected by comparing such values.
Japanese Laid-Open Application No. 63-135761 discloses the use of an electrical expansion valve, wherein a refrigerant medium gas leak is detected from a relationship between an opening degree of the expansion valve and the evaporation temperature.
Japanese Laid-Open Application No. 63-238364 proposes sensing the evaporator outlet temperature at a time when the compressor is halted, for detecting a refrigerant medium gas leakage.
U.S. Pat. No. 5,150,584 to Tomasov et al. discloses detecting a refrigerant medium gas leak from a relationship between inlet evaporation temperature and the outlet evaporation temperature of an evaporator, and the compressor surface temperature.
U.S. Pat. No. 5,301,514 to Bessler et al. discloses detecting a refrigerant medium gas leak from a relation between an expansion pressure valve opening degree and evaporation temperature.
U.S. Pat. No. 5,713,213 to Nobuta et al. uses not only evaporation temperature but also a relationship with the halted state of the compressor for accurate detection of a refrigerant medium leak.
Finally, German Patent Document DE 3 913 521 by Hemm discloses detecting a refrigerant medium gas leak by means of a calculation using the compressor inlet refrigerant medium pressure and refrigerant medium temperature.
The above known techniques, although suggesting a relationship of evaporation temperature with a refrigerant gas leak, nevertheless possess important differences which make them impractical for use in a remote factory installed environment which is an indispensable requirement of the above-described chiller unit. In particular, since these known techniques are primarily intended for use in automobiles, a continuous time-based monitoring of parameters is not readily possible. Moreover, because an automobile encounters all kinds of environmental changes in temperature, humidity and the like, it is difficult to reliably detect an evaporation temperature that is not influenced by environmental conditions, and reliably determining temperature changes in the evaporation temperature alone, not affected by environmental conditions, is difficult if not impossible in an automotive situation.
In contrast to the prior techniques discussed above, the present invention has an object of detecting a refrigerant leak using remote maintenance technology, for chiller units that are disposed in a substantially constant temperature factory setting, where the influence of environmental temperature is largely constant and therefore can be accounted for in a predictable way. Therefore, the present invention enables a simple and low cost method of detecting or predicting a refrigerant gas leak, on the basis of a relationship between the evaporation temperature and at least one of 1) atmospheric temperature in the vicinity of a condenser, 2) condenser cooling water temperature, or 3) the temperature of the refrigerant as it passes through the condenser (i.e., refrigerant condensing temperature), in a refrigeration circuit. Stated otherwise, the present invention enables a refrigerant gas leak to be reliably detected on the basis of the evaporation temperature while understanding the relationship thereof to atmospheric temperature, condenser cooling water temperature and/or refrigerant condensing temperature, using a simple thermocouple or other temperature detecting means, thereby lowering cost.
A further object of the present invention is to enable chiller units to be monitored continuously using remote maintenance technology, with the aim of predicting an incipient refrigerant gas leak using a relationship between evaporator temperature and the quantity of refrigerant which circulates in the refrigeration circuit. Data on the evaporation temperature, detected using the simple thermocouple means described in the preceding paragraph, along with at least one of atmospheric temperature, condenser cooling water temperature or refrigerant condensing temperature, is sampled periodically and transmitted over a network (such as the Internet or an intranet, by electronic mail, telephone lines or any other means for enabling data transmission) to a monitoring and servicing facility. Analysis of the data at the monitoring and servicing facility is performed on a periodic time basis to detect a refrigerant gas leak, and when so detected, maintenance personnel can be dispatched to the remote factory location for servicing or repair of the chiller units.
The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative example.